It is known in the art relating to control circuits to provide a control circuit to control the current through an inductive load. The current through an inductive load can be increased by providing a positive voltage across the load and the current can be decreased by providing a negative voltage across the load. In other words, an energy source must be applied to an inductive load for increasing the current and an energy sink is needed across it for reducing the current. When only a unipolar power source, such as a battery or other DC source, supplies power to an inductive load which has one end connected to the battery ground, some special means are necessary to generate the negative voltage during decreasing currents.
Most conventional circuits used to control the current through inductive loads use two switches to increase and decrease the current, however, the decrease in load current can be relatively slow. For a faster decrease in load currents, a zener diode or an external resistor has been added in series with the second switch. However, this may create additional loss even when the load current is maintained at a fixed value by pulse width modulation of the output voltage and, therefore, cannot be used for output currents greater than a few amperes.
One application for such control circuits is in a Magneto-Rheological (MR) fluid-based variable damping device developed for automotive suspension control applications. In such a device, a continuously variable damping force is achieved by varying the current through a coil that controls the magnetic field applied across the fluid passing through an annulus. Another application for the control circuit is a servo-valve which uses current through a coil to control the pressure across a valve. Other applications of MR devices include clutches for transmission, steering and fan control, engine mounts and valves. The present invention disclosed herein provides better controllability of magnetically operated devices using a coil.